As shown in FIG. 1, an armored electrical cable 10 used, for example, to wire buildings has insulated wires 12 encased in a helically wound steel sheath 14. To install the cable, the wires at each end of the sheath are stripped of insulation 16, and the exposed conductors 18 are connected to terminals or other wires inside of a junction box, switch box or other enclosure.
The installer knows which connections to make at each end of the cable because the wire insulations are color-coded. For example, a ground wire may have one color, and wires carrying different phases of AC power could have other colors. The insulation colors are often dictated by industry practice. A cable used for a particular purpose, such as to wire three-phase 277-volt power, typically has several (e.g., four) internal wires and a particular combination of color-coded insulations on the wires. The insulation colors may comply, for example, with the B-O-Y (brown, orange, yellow) convention, in which brown, brown and orange, or brown, orange and yellow, are used depending on the number of internal wires that need to be marked in the cable. In addition, common and ground wires in the cable may have gray and green insulations. The installer (or someone who maintains the cable after installation) can easily identify the purpose of a given cable (e.g., that it is a 277-volt cable) by the predefined combination of insulation colors that are associated with that purpose.
As shown in FIG. 2, once the installation is done, the sheath 14 and the junction boxes 20 at both ends of the cable hide the internal wires from view.
The sheath of a cable can be marked to indicate the function of the cable as described in U.S. Pat. No. 5,350,885, incorporated by reference. The markings can include color-coded coatings and patterns.